1. Technical Field
The disclosure relates to active aerodynamic fairings or shrouds for vehicles, and more particularly to a power source for controlling the extension and retraction of such shrouds.
2. Description of the Problem
Aerodynamic drag contributes greatly to fuel consumption by tractors pulling trailers at highway speeds. The gap between the tractor and trailer tends to trap air, creating a low-pressure wake behind the tractor, resulting in a net pressure difference creating drag. It also exposes portions of the front of the trailer to the direct impact of air further contributing to decreased fuel economy. The gap distance between the tractor-trailer combination has been dependent on the position of what is known in the art as a fifth wheel. The fifth wheel is a bearing and serves as a coupling between the tractor and trailer. The position of the fifth wheel is adjusted to accommodate different weight distributions based on the load of the trailer. The gap distance typically varies from about 36 to 48 inches. The drag coefficient and effective frontal area of the trailer is dependent on the gap distance. More specifically, the larger the gap distance, the larger the drag coefficient and exposed frontal area of the trailer, and conversely, the smaller the gap distance, the smaller the drag coefficient.
The gap causes the formation of a turbulent air mass creating a low-pressure wake behind the tractor, decreasing the fuel efficiency of the vehicle. The goal in aerodynamic design is to produce shapes that delay air separation. Maximum efficiency is achieved when airflow remains attached and moves parallel to the side of the vehicle such that air separation from the tractor is reduced and a constant and smooth airflow along the side of the vehicle is achieved.
One solution has been to close the gap between the sides of the cab and the sides of the trailer using cab extenders or fairings. Fixed cab extenders are planar members which extend aft longitudinally from a back end of the tractor substantially parallel with the sides of the tractor and upper fairings which slope upwardly from the cab roof to the front leading edge of the trailer. Ideally, the fixed cab extenders would extend across the entire gap between the tractor and trailer, which, as stated above, typically varies from 36 to 48 inches, to obtain the maximum aerodynamic gain. However, if the fixed cab extenders were configured as described, as the tractor turned relative to the trailer, the trailer could collide with impact and damage the extenders. Various solutions to this problem have been proposed.
Some previously developed fixed cab extenders were positioned to leave substantial clearance between the rearmost vertical edge of the fixed cab extender and a front end of the trailer. This clearance between the front end of the trailer and the fixed cab extenders prevented contact during sharp, typically slow speed turns. Of course, the wider the gap left, the less effective the extender is, though any extension provided some benefit. Other methods of addressing the issue were proposed, including various types of deployable cab extender allowing changing the clearance space between the tractor and trailer at high speeds so that it would fully deployed at highway speeds to improve fuel economy, and retracted at low speeds to allow the tractor trailer truck to maneuver. It was also recognized that a need existed for a cab extender that was adjustable in length to accommodate the variability in spacing encountered between the tractor and trailer.
One previously developed attempt at fulfilling some of these needs is disclosed in U.S. Pat. No. 3,711,146 issued to Madzsar (hereinafter “Madzsar”). Madzsar teaches adjusting the length of the cab extenders based upon a sensed amount of articulation between a tractor and trailer.
U.S. Pat. No. 6,846,035 issued to Wong, et al. provided an adjustable length cab extender disposed in a gap located between a tractor and a trailer. The dynamic cab extender was configurable between a deployed position, a stowed position, and an extended position. In the deployed position, the dynamic cab extender was oriented substantially coplanar with a side of the vehicle in a gap extending between a back end of the tractor and a front end of the trailer. In the stowed position, the dynamic cab extender was stowed behind the back end of the tractor. In the extended position, the dynamic cab extender was oriented substantially coplanar with the side of the vehicle in the gap. A length of the dynamic cab extender when in the extended position exceeds the length of the dynamic cab extender when stowed. Automatic adjustment of the length of the cab extender was provided in response to changes in vehicle speed. This included automatically adjusting a longitudinal length of the dynamic cab extender to selectively position a trailing edge of the dynamic cab extender a selected distance from a front end of the trailer when the sensed speed of the tractor exceeds a selected speed.